1. Field of the Invention
The present invention relates generally to methods and devices for the nondestructive evaluation of materials. The present invention relates more specifically to a magnetostrictive sensor based system for the inspection of pipeline structures from an in-line inspection vehicle.
2. Description of the Related Art
The use of magnetostrictive sensors (MsS) in the nondestructive evaluation (NDE) of materials has proven to be very effective in characterizing defects, inclusions, and corrosion within various types of ferromagnetic and non-ferromagnetic structures. A MsS launches a short duration (or a pulse) of elastic guided waves in the structure under investigation and detects guided wave signals reflected from anomalies such as defects in the structure. Since guided waves can propagate long distances (typically 100 ft or more), the MsS technique can inspect a significant volume of a structure very quickly. In comparison, other conventional NDE techniques such as ultrasonics and eddy current inspect only the local area immediately adjacent to the probes used. Therefore, the use of magnetostrictive sensors offers a very cost effective means for inspecting large areas of steel structures such as strands, cables, pipes, and tubes quickly with minimum support requirements such as surface preparation, scaffolding, and insulation removal. The ability to use magnetostrictive sensors with little preparation of the object under inspection derives from the fact that direct physical contact between the sensors and the material is not required.
Efforts have been made in the past to utilize magnetostrictive sensor technologies in association with the inspection of both ferromagnetic and non-ferromagnetic materials. Included in these efforts are systems disclosed in U.S. Pat. Nos. 5,456,113, 5,457,994 and 5,501,037 which are each commonly owned by the assignee of the present invention. The disclosures of U.S. Pat. Nos. 5,456,113, 5,457,1994 and 5,501,037 provide background on the magnetostrictive effect and its use in NDE and are therefor incorporated herein by reference. These efforts in the past have focused primarily on the external inspection of piping, tubing and steel strands/cables wherein the nature of the structure is such that uninterrupted internal access to the pipe wall is very limited. While these systems and their external application to longitudinal structures find significant applications, there are yet other inspection techniques structures that could benefit from the use of magnetostrictive based NDE.